It warned that the neighbour's decision to not vaccinate, "puts anyone at risk if they are medically fragile, immunocompromised, or out of date in their vaccinations".

It goes on to warn others to avoid her.

"Please use caution when sharing work or personal space with this individual, eating foods prepared by this individual, or attending gatherings at this individual's house if you or the people who are important to you fall into medically at-risk categories."

"The unvaccinated threaten infants"

The letter then addresses the risk of the unvaccinated on people who are immune-compromised or can't be vaccinated, such as babies, the elderly and patients undergoing chemotherapy.

"The unvaccinated pose a unique threat to infants, who often don't yet have a full course of vaccinations completed, and can quickly become deathly ill or die," the letter states.

It also points out the terrifying number of measles outbreaks across 15 US states.

NSW Health issued a measles warning at the start of the year following an outbreak in Sydney.

"Nearly all outbreaks of disease were started by unvaccinated individuals, who pass along vaccine-preventable diseases to those without adequate protection," the letter reads.

"People who don't believe in vaccines often hold other views that are at odds with widely accepted facts related to science and medicine."

The letter finishes with a link to a site that tracks outbreaks of vaccine-preventable diseases and a warning to "protect yourself, your family, and your community by using caution when interacting with these people".

Get the facts

In Australia, the Government's 'Get the facts about immunisation' campaign supports parents, and those with children under the age of 5 years, by explaining the benefits of vaccination and addressing misconceptions.

The campaign can be accessed on the Department of Health website.

There have also been multiple cases of measles in Australia this year, including in Melbourne, Sydney and Perth.

This article originally appeared on Kidspot and was reproduced with permission